August 6, 2020
Air pollution is linked to an increased risk of heart attacks, strokes, respiratory disease, cancer and early death. It has also been tied to detrimental brain changes typical of Alzheimer’s disease and other forms of dementia. Now a new study reports that eating fish may help protect the brain against the damaging effects of air pollution.
For the study, scientists looked at 1,315 women ranging in age from 65 to 80 who lived in different areas of the country. The women filled out detailed questionnaires about their typical daily diets, including consumption of seafood. They also had blood tests to measure red blood cell levels of omega-3 fatty acids, the healthy fats found in fish.
All the women also had MRI scans to measure the volume of white matter in the brain, an indicator of overall brain health. Indeed, brain shrinkage is often observed with advancing age and is also tied to the memory and thinking problems that presage Alzheimer’s disease. The findings were reported in Neurology, the medical journal of the American Academy of Neurology.
They found that women who had the highest blood levels of omega-3 fatty acids — equivalent to eating more than one to two servings of baked or broiled fish or shellfish a week — had greater volumes of white matter in the brain. Even a single eight-ounce serving of fish a week was associated with greater white matter volume, regardless of blood levels of omega-3s.
Using data from the Environmental Protection Agency, the researchers tracked pollution levels at the women’s home addresses over a three-year period. Among older women who lived in areas with high levels of air pollution, those who had the lowest levels of omega-3 fatty acids in their blood had more brain shrinkage than women who had the highest levels. The adverse effects of air pollution on brain volume were much smaller in women with the highest levels of omega-3s.
“Fish are an excellent source of omega-3 fatty acids and easy to add to the diet,” said study author Dr. Ka He of Columbia University in New York. “Omega-3 fatty acids have been shown to fight inflammation and maintain brain structure in aging brains. They have also been found to reduce brain damage caused by neurotoxins like lead and mercury.”
Tiny airborne pollutants called PM2.5 particles, which are about 1/30th the width of a human hair, have been traced to the damaging brain changes of air pollution. (PM stands for particulate matter, and 2.5 refers to the size of the particles, 2.5 micrometers.) The particles are found in traffic exhaust and industrial smoke and are easily inhaled into the lungs, where they can enter the bloodstream and find their way into the brain.
Earlier studies have found that women exposed to higher levels of air pollutants experienced greater declines in memory than their counterparts who breathed cleaner air, and that long-term exposure to pollution contributed to the equivalent of about a two-year decline in brain function. Brain wasting might set the stage for an earlier onset of dementia.
Animal studies have also recorded higher levels of brain inflammation in animals exposed to polluted air. Increasingly, scientists believe that inflammation may play an important role in Alzheimer’s, heart disease and other chronic ailments.
The study is important because at present, little can be done to stop the progression of Alzheimer’s disease, and any lifestyle measure, including exercise or diet, may help to slow the onset of illness.
“Our findings suggest that higher levels of omega-3 fatty acids in the blood from fish consumption may preserve brain volume as women age and possibly protect against the potential toxic effects of air pollution,” said Dr. He. “It’s important to note that our study only found an association between brain volume and eating fish. It does not prove that eating fish preserves brain volume. And since separate studies have found some species of fish may contain environmental toxins, it’s important to talk to a doctor about what types of fish to eat before adding more fish to your diet.”
Toxins can include mercury, found in large fish like swordfish and some kinds of tuna. The Food and Drug Administration provides guidelines about eating fish and the best and worst fish to eat at https://www.fda.gov/food/consumers/advice-about-eating-fish.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Cheng Chen, Pengcheng Xun, Joel D. Kaufman, et al: “Erythrocyte omega-3 index, ambient fine particle exposure and brain aging.” Neurology, July 15, 2020